R help - Sep 2004 - An index of all possible combinations of variables in a data fram e

Hello list
 
Does anybody know of any way to create an index of all the possible
combinations of variables (factors) in a data frame? ie for 3 factors A, B &
C we have 
 
A
B
C
AB
AC
BC
ABC
 
which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
 
I realise that a function like model.matrix does this, but how to get the
seqence of the index?
 
Any help would be greatly appreciated.
 
Regards
 
Alan Simpson
Roberts Research Group
 

	[[alternative HTML version deleted]]

Alan Simpson <alan.simpson <at> robertsresearch.com.au> writes:

: Does anybody know of any way to create an index of all the possible
: combinations of variables (factors) in a data frame? ie for 3 factors A, B
&
: C we have 
: 
: A
: B
: C
: AB
: AC
: BC
: ABC
:  
: which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
: 
: I realise that a function like model.matrix does this, but how to get the
: seqence of the index?
: 

Is this what you are looking for?

R> attributes(terms(~ a * b * c))$term.labels
[1] "a"     "b"     "c"     "a:b"  
"a:c"   "b:c"   "a:b:c"

Hi Alan,

you could also try the following function which has been submitted to 
s-news some time ago:

powerSet <- function(x){
 if(length(x)==0) return(vector(mode(x), 0))
 x <- sort(unique(x))
 K <- NULL
 for(m in x) K <- rbind(cbind(K, FALSE), cbind(K, TRUE))
 out <- apply(K, 1, function(x, s) s[x], s=x)[-1]
 names(out) <- NULL
 return(out)
}

powerSet(1:5)

I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Alan Simpson" <alan.simpson at robertsresearch.com.au>
To: <r-help at stat.math.ethz.ch>
Sent: Tuesday, September 28, 2004 6:51 AM
Subject: [R] An index of all possible combinations of variables in a 
datafram e

> Hello list
>
> Does anybody know of any way to create an index of all the possible
> combinations of variables (factors) in a data frame? ie for 3 
> factors A, B &
> C we have
>
> A
> B
> C
> AB
> AC
> BC
> ABC
>
> which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
>
> I realise that a function like model.matrix does this, but how to 
> get the
> seqence of the index?
>
> Any help would be greatly appreciated.
>
> Regards
>
> Alan Simpson
> Roberts Research Group
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>

Alternatively you can use the combinations() function in gregmisc.

library(gregmisc)
n <- 3
sapply(1:n, function(x) apply(combinations(n, x, LETTERS[1:n]), 1, 
paste, collapse="") )

Here is the same code written with a for loop
n <- 3
out <- NULL
for(i in 1:n){
  tmp <- combinations(n, i, LETTERS[1:n])
  out <- c(out, apply(tmp, 1, paste, collapse=""))
}
out
[1] "A"   "B"   "C"   "AB" 
"AC"  "BC"  "ABC"




On Tue, 2004-09-28 at 08:38, Dimitris Rizopoulos wrote:
> Hi Alan,
> 
> you could also try the following function which has been submitted to 
> s-news some time ago:
> 
> powerSet <- function(x){
>  if(length(x)==0) return(vector(mode(x), 0))
>  x <- sort(unique(x))
>  K <- NULL
>  for(m in x) K <- rbind(cbind(K, FALSE), cbind(K, TRUE))
>  out <- apply(K, 1, function(x, s) s[x], s=x)[-1]
>  names(out) <- NULL
>  return(out)
> }
> 
> powerSet(1:5)
> 
> I hope it helps.
> 
> Best,
> Dimitris
> 
> ----
> Dimitris Rizopoulos
> Ph.D. Student
> Biostatistical Centre
> School of Public Health
> Catholic University of Leuven
> 
> Address: Kapucijnenvoer 35, Leuven, Belgium
> Tel: +32/16/396887
> Fax: +32/16/337015
> Web: http://www.med.kuleuven.ac.be/biostat/
>      http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
> 
> 
> ----- Original Message ----- 
> From: "Alan Simpson" <alan.simpson at
robertsresearch.com.au>
> To: <r-help at stat.math.ethz.ch>
> Sent: Tuesday, September 28, 2004 6:51 AM
> Subject: [R] An index of all possible combinations of variables in a 
> datafram e
> 
> 
> > Hello list
> >
> > Does anybody know of any way to create an index of all the possible
> > combinations of variables (factors) in a data frame? ie for 3 
> > factors A, B &
> > C we have
> >
> > A
> > B
> > C
> > AB
> > AC
> > BC
> > ABC
> >
> > which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
> >
> > I realise that a function like model.matrix does this, but how to 
> > get the
> > seqence of the index?
> >
> > Any help would be greatly appreciated.
> >
> > Regards
> >
> > Alan Simpson
> > Roberts Research Group
> >
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> >
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Yet another solution might be to abuse expand.grid:

dat <- expand.grid(rep(list(c(FALSE,TRUE)), 3))
apply(dat, 1, function(x)which(x))

This gives you a list of the numeric column indices, including an empty
component at the beginning corresponding to none of the variables
present.

Alan Simpson wrote:
> Hello list
>  
> Does anybody know of any way to create an index of all the possible
> combinations of variables (factors) in a data frame? ie for 3 factors A, B
&
> C we have 
>  
> A
> B
> C
> AB
> AC
> BC
> ABC
>  
> which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
>  
> I realise that a function like model.matrix does this, but how to get the
> seqence of the index?
-- 
Christopher Jackson <chris.jackson at imperial.ac.uk>, Research Associate,
Department of Epidemiology and Public Health, Imperial College
School of Medicine, Norfolk Place, London W2 1PG, tel. 020 759 43371